Rigol electronic load working principle

[Roeland]

I am working with a Rigol DL3021A DC electronic load and to explain some of the measurements result I want to know whats the working principle of the load.
is there a physique resister or is there a sort of switch to regulate the output load?
can some help me with this?

[ledtester]

There is usually a bank of MOSFET transistors which are used to control the current drawn by the load.

Here Dave does a teardown of the Rigol load (started at 7:28):

https://youtu.be/Tk_3rYKWIIg?t=7m28s

The MOSFETs are the transistors attached to the big heatsink.

In this video Dave explains how an op-amp controlled constant-current load works:

https://youtu.be/8xX2SVcItOA?t=2m15s

[MarkF]

Here is the circuit for a HP-6060 Electronic Load. (I would expect the Rigol to be similar.)

https://www.eevblog.com/forum/projects/my-first-power-supply-182985/?action=dlattach;attach=846488;image